As shown in FIG. 1, a conventional packaging structure for a laser diode 10, comprises: a laser diode chip 110, an optical axis 101 of a light beam center capable of emitting a cone-shaped laser beam 100, a submount 120, and a heat-conducting base 130, wherein the submount 120 and the heat-conducting base 130 are made of copper alloys, the laser diode chip 110 is a semiconductor chip, both of which are often bonded by an adhesive 118. The submount 120 is loaded with the laser diode chip 110 and conducts heat to the heat-conducting base 130, wherein the heat-conducting base 130 is not large. As a result, the air contact area is not large enough to dissipate the heat to the air by itself and the heat has to be dissipated by a main surface of the heat-conducting base 192 contacting with a bigger external heat dissipating body 191 (e.g., a body shell made of aluminum or a specialized heat-dissipating fin). To improve the efficiency of heat dissipation, the main surface of the heat-conducting base 192 is required to be large and even, and it is common that the main surface of the heat-conducting base 192 is parallel to the surface of a window glass 105 (both of which are vertical to the optical axis 101) for installing the mounting mechanism of the window glass 105 and the main surface of the heat-conducting base 192, so that the contact area between the main surface of the heat-conducting base 192 and the external heat dissipating body 191 can be expanded to improve the heat-conducting efficiency. Those aforementioned mechanisms are common in the packaging for low or medium power laser diodes. However, the aforementioned packaging structure is difficult to be implemented for high-power laser diodes, because high-power laser diodes generate a much larger amount of heat. Furthermore, there are two or three pins next to the submount to connect the laser chip by gold wire bonding. Because the pins need to be as close to the laser chip as possible, there is no space for the submount to expand; hence the submount has to be as small as possible, rendering formation of a bottleneck throughout the entire heat-conducting pathway. As show in FIG. 1, the faying plane 190 (cross section A-A) between the submount 120 and the heat-conducting base 130 is too small and the heat-conducting area cannot be expanded. FIG. 2, including FIG. 2A and FIG. 2B, wherein the unit shown in the figures is mm, shows a packaging structure for a laser diode 20. FIG. 2A shows a conventional TO-5 packaging structure for a laser diode 20 comprising: a laser diode chip 210 which can emit a laser beam 200 having an optical axis 201, a submount 220, a heat-conducting base 230 and pins 227, wherein the maximum area of the faying plane 290 (cross section A-A) between the submount 220 and the heat-conducting base 230 is approximately 1.3 mm×3.3 mm=4.29 mm2, no more than 6 mm2. Because the area of the faying plane 290 (cross section A-A) between the submount and the heat-conducting base is so small that it becomes a bottleneck of the heat conduction, it is difficult to conduct the heat from the laser diode chip 210 to the heat dissipating body, that is, the heat is conducted by the heat-conducting base 230, through a main surface of the heat-conducting base 292 to an external heat dissipating body.
FIG. 2B shows another conventional C-Mount packaging structure for a laser diode 20′, which comprises generally the same main components as shown in FIG. 2A, and the area of the faying plane 290 (cross section A-A) for heat conduction is 1.8×mm×2.0 mm=3.6 mm2, no more than 6 mm2. Meanwhile, in FIG. 1 and FIGS. 2A and 2B, the same components are denoted by changing the numbers from 1xx to 2xx.
According to physics, one skilled in the art should know that the rate of heat conduction is proportional to the heat-conducting area, and because the heat-conducting area of the submount provided by the conventional packaging structure for a laser diode (the aforementioned area of the faying plane) is too small, the large amount of heat generated by the laser diode chip is difficult to be dissipated through the submount to the heat-conducting base; furthermore, because the submount is installed in a limited space, the heat-conducting area cannot be expanded as necessary for improving the heat-conducting efficiency. The small heat-conducting area of the submount is the bottleneck of the heat conduction of the packaging of laser diodes.
Furthermore, as shown in FIG. 1 and FIG. 2, the conventional laser diodes are packaged cylindrically and individually, as previously discussed the heat-conducting area of the submount cannot be expanded inside the package, and there is no space to accommodate another laser diode chip, nor other electronic components. Apparently, the conventional packaging is not suitable for a device that needs more than one laser diode, and there is no space for installing other electronic components to improve performance.
Also, FIG. 1 and FIG. 2 show conventional packaging structures for laser diodes 10 and 20, wherein an optical axis 101, 201 of the laser beam 100, 200 is emitted vertically to the main surface of the heat-conducting base 192, 292, rather than being emitted in parallel. Besides, the existing packaging methods for laser diodes cannot provide additional space in the existing packaging structure to improve the performance of the laser diode, for example, an additional photo diode for detecting the optical power of laser diodes, an electrostatic discharge protection diode, and/or a reverse bias voltage protection diode. Besides, one skilled in the art also knows the LED chip emits light from the upfront surface instead of edge, it is easy for the LED to be packaged on a large plate for large amount heat dissipation; however, most of the laser diode chips emit light from the edge instead of the upfront surface, it is difficult for them to be packaged on a large plate. Consequently, conventional laser diode chips that emit light from the edge are not packaged on a large plate and cannot be provided with large size heat-conducting components.
Therefore, there is a high demand for a packaging structure which can solve the problems that conventional packaging structures for laser diodes have, especially the heat-conducting problems associated with packaging structures for medium or high power laser diode chips which emit light from the edge and generate large amount of heat.